“…34−38 However, it is still very challenging to study some large molecular systems computationally, such as infinite crystal solids containing weak interactions, by any of the current quantum-mechanical method, since it is necessary to use reasonably large basis sets and high-order correlation corrections simultaneously 39−41 in those large molecular systems. We have developed a new ab initio cyclic periodic wave function (CPWF) method 42 to solve some of the problems involved in these systems. In order for the method to be used to study reasonably large molecular systems in the crystal state, where relatively weak intermolecular interactions may be important, we will apply the method at the AM1 43 and PM3 44,45 semiempirical levels of approximation.…”